Next Upgrade Dilema - Camera or Guiding?

[PottyMonster]

Hi All, I'm fairly new to imaging and enjoying the journey, however I'm on a budget in a fairly light polluted area and have a dilema as to what upgrade path to persue.

Currently using a Skywatcher 250PDS on a HEQ5 mount with a (unmodified) Canon 650D SLR and would like to move to narrowband imaging, however I'm not sure if I should get autoguiding working by buying a tracking camera and some narrow band filters that I can use with my SLR, or if I should get a new imaging sensor and filters but have it unguided?

I'm fairly confident I've got polar alignment working well and can get exposures up to around 1m without star trails, however at that sort of exposure time I'm saturated with light pollution. Eventually I'll upgrade the entire system, I just don't have the budget to do it all at once. Would 1 min ungided with a more sensive astro camera and narrow band filters give ok results? I'm considering something like a ZWO ASI178 mono.

I do have a secondary question as to filter sizes. I know I'm lazy and eventually will want to get a filter wheel so any filters I get now I'd like to ensure I can get value out of later. From what I can tell 1.25" filters aren't a option for SLRs but are fine for astro cameras?....however 2" filters are expensive. Would 31 or 36mm filters be a good compromise to fit in a filter wheel?

Any advice greatly appreciated. I'm not aiming for Hubble quality photos, but trying to be forward looking and sensible.

[upahill]

If it was me I would go for guiding. Makes life so much easier and polar alignment is rarely perfect so if you are setting up each time, having guiding can really help.

You could maybe get a clip in light polution filter for the dslr.

The path I chose was Mount -> OTA -> DSLR -> Guiding -> Focus -> Filter Wheel -> Filters -------> Next step is a decent camera.

[Star101]

On a budget route. Although maybe someone can advise on how good they are... Search for Quadband DSLR filter. Maybe its a short term solution before you spend too much!! This should give good results in light polluted areas.

 

[PottyMonster]

29 minutes ago, Star101 said:

On a budget route. Although maybe someone can advise on how good they are... Search for Quadband DSLR filter. Maybe its a short term solution before you spend too much!! This should give good results in light polluted areas.

 

I don't mind spending some money on filters I'll get use out of later, I'd just like them to be compatible with a more sensitive astro camera at a later date. From what I can tell though 1.25" filters aren't great for a SLR.

[upahill]

I went down the 36mm route because of the same concerns. Didn't want to buy something too small, but couldnt quite justify the 2" filters.

I now have a ZWO 7x36 with Baader 36mm Unmounted filters - can't comment on them as haven't used them yet, but from what I could gather they would give me a wide range of scope/cam combinations in the future if I wanted to change setup. The most likely candidate for my camera is the ASI1600 so it made sense to get the ZWO stuff too.

Weirdly I had never considered hooking up the slr to that combo though - or even if its possible. 🤔

The quadband DSLR filter is a good idea though if it will be a while before getting a dedicated astro camera. I have heard some pretty high praise for the AltairAstro ones.

[adoldesa]

Hi there,

guiding will surely help, especially with a 250P which has a fairly long focal. There are good deals online for a guide scope and a guide camera for about £200 (I use the ZWO120mm mini). I used a DSLR for about 12 months using a good light pollution filter (I am in Class 5 skies), for instance an IDAS or a SkyTech LPro Max are good choices and the can be used with dedicated astro cameras. Personally, I upgraded the mount and the guiding before moving to a dedicated CMOS cooled camera, the DSLR will give you great results if you can guide for 2-3 min with a good filter.
 

[wuthton]

Your 250pds is a beautiful scope but it's not your friend for narrowband imaging. The focal length literally magnifies even the slightest jiggle and it's physical size makes those jiggles more likely to happen, guided or not. Beautifully crafted optics with perfect colour correction are wasted on narrowband imaging, if focused you could take a great image through the bottom of a jam jar but what it does require is time and no jiggles.

Narrowband filters are expensive and the shorter the bandpass the more expensive they get. At longer focal lengths the difference between cheaper and more expensive filters becomes much more pronounced, you get beautiful tight stars with some Astrodons and comparatively bloated stars with 7nm Baaders. Conversely at shorter focal lengths and wider fields of view the differences are greatly reduced. You only need to buy the filter size recommend for your camera, buying any bigger is a waste of money. My Atik 314 has a tiny chip so only requires 1.25", My Moravian G2 has a bigger, KAF-8300 chip, I can get away with 31mm without any vignette.

I've only ever used CCD cameras but if I were buying a camera today I'd be giving the current crop of CMOS some lusty glances. You can get similar results to a CCD but with shorter exposures, less time then less chance of jiggles. Your integration time is similar to CCD but made up of more but shorter exposures.

If you're managing a minute at 1.2m then you'll manage and age unguided if you reduce your focal length. Beg, borrow or steal a prime camera lens with a manual aperture ring (Pentax Super Takumar fit well) and add a cooled, mono CMOS camera with a cheap Ha filter, strap it to your HEQ5 and point it at Orion for 2 minuites, you won't be disappointed.

 

Edited December 1, 2019 by wuthton

[tooth_dr]

I’ve had good success with my 250px scope including using a 12nm Ha filter.

My recommendation would be guiding, using a finderscope to guide with to minimise weight. You are prob getting close to limit on the mount.

The FOV with the 178 will be a lot smaller. It wouldn’t be my choice

 

[tooth_dr]

Plus you will be very much over sampling with the 178 at 0.41”/px

[Nigella Bryant]

I'd go for guiding first with an added light pollution filter and get the slr modded. I use an old modded Canon 1000d with a D2 Idas filter but I have led street lights near me. 

[wimvb]

+1 for guiding first. For nb as well as for general image improvement, you need longer subs, and without guiding you won't get there. To combat LP, you can invest in a good lp filter.

After that a cooled (cmos) camera with filter wheel. Choose the camera to give you a pixel scale of 1"/pixel or a little less. 

Pixelscale = 206*pixel_size/focal_length

Pixel_size in micrometers, focal_length in millimeters

As @tooth_dr showed, use a field of view calculator to figure out sensor size. 

[PottyMonster]

Thanks everyone, greatly appreciate all of the replies. Guiding it is!